A student at Yokobane High School. Together with Rei, he had hired Hamatora to find their missing teacher, Yasuo Kitazawa. Later, he and Rei took part time jobs at a hot spring, where they once again crossed paths with the Hamatora.
Theo had been bullied until a month before the current storyline by five male students in his high school ( the last incident occurring in an arcade ). This lead him to the thought of jumping off the school's roof multiple times after the event. He even decided to tell his parents and teachers about his problem but was threatened by the aforementioned bullies, saying that if he told anyone else, they'd go to Rei and mess her up ( This showed that he cared for her ). However, his Fine Arts teacher, Yasuo Kitazawa, took the problem to the school board and ended the problem. According to Theo, Kitazawa-Sensei was "the only light in his darkness".
Theo is a very hot headed individual as shown by him getting angry at the slightest thing. He has shown open attraction to males, meaning he is gay. He had shown past affection for Kitazawa (before seeing his true colors) and he had a temporary crush on Hasuda Arai (before learning he was a criminal). This also shows he has bad taste in men, and tends to prefer older mature ones.
The two are very close, and Rei is almost always seen by his side or somewhere else nearby. They share a relationship akin to childhood friends or siblings.
After getting Nice's help in solving the cold case of what happened to his teacher's murder, he was a frequent stayer at the Hamatora hideout alongside Rei, in which they both are interested in Nice and the rest of the Hamatora's daily affairs.
Kitazawa was Theo's teacher at school, and such is viewed with a lot of respect. Theo admires him for both his work ethic and his compassion for others, and is very grateful for the help he contributed when stopping the bullies. The two were close, as shown by Theo's reaction to his death. However, Theo begins to feel remorse for his teacher when he finds out that he was the ring-leader behind the bullying, and thus becomes angry and depressed. He is shown destroying an arrangement set to honour Kitazawa's death in a fit of rage.
Murasaki was one of the members of Hamatora during the time investigating the murder of Theo's teacher, thus beginning the bond
After the incident with Freenum, Theo and Rei visited him in the hospital, giving him glasses as a gift (Clearly as a joke), causing the rest of Hamatora to laugh, including Birthday who accidentally presses on the eject button, causing Murasaki to fly out of bed. After the ordeal, Rei, Hajime and Theo left the hospital in order to go to a flower shop, in which he witnessed Hajime being kidnapped by Momoka.
Theo worked for Hasuda Aria in a spa, who alluded Theo with his sweat quirk.